The formation of ice on the wings of an airplane can reduce the lift and increase the drag by degrading the performance of the airfoil. Additionally, the ice may break away from the wing and be ingested by an engine, possibly causing a failure of the engine and endangering the safety of the passengers of the aircraft. To remove and prevent the build-up of ice on the wings, the skin of the wings can be sprayed with a fluid that has a low freezing point, such as a glycol. In cold climates the wings are typically sprayed at the airport before takeoff. The glycol forms a protective layer on the aircraft. The glycol has low shear strength and allows the ice to be sheared from the wings. Wings are sprayed with a heated dilute glycol solution (propylene, ethylene or a mixture of the two, in water). The solution typically also holds wetting agents, rust inhibitors, flame retardants, thickeners and other materials, depending on the Class of the solution being used, and depending on the nature of other fluids that are deposited to airport runways and roads during daily operations.
Conventional aircraft deicing by hot deicing fluid (Type I) washdown from ground or mobile boom systems has been in use for decades with no basic changes to this technology other than refinements to the deicing fluid heating and application systems. Some of the patents covering conventional deicing and its refinements are as follows U.S. Pat. No. 3,243,123, to D. M. Ingraham, et. al., issued Mar. 29, 1966; U.S. Pat. No. 4,073,437 to Thornton-Trump, issued Feb. 14, 1978; U.S. Pat. No. 4,826,107 to Thornton-Trump, issued May 2, 1989 and U.S. Pat. No. 5,028,017, to Simmons, et al., issued Jul. 2, 1991. Other publications describe various deicing systems to improve the deicing process, either by reducing or eliminating the use of glycol, or by applying glycol in a more efficient manner such that the glycol usage is reduced for instance: U.S. Pat. No. 5,244,168 to Williams, issued Sep. 14, 1993 for A Methodology And Apparatus For Forced Air Aircraft Deicing and U.S. Pat. No. 5,104,068 to Krilla et al., issued Apr. 14, 1992.
Presently, aircraft deicing is carried out by applying glycol based deicing fluids, which may be propylene glycol, ethylene glycol or a mixture of the two glycols.
These fluids are sprayed on aircraft to lift accumulated ice and it is believed that propylene glycol prevents ice buildup. Numerous composition and method patents exist on this application and have been disclosed in U.S. Pat. No. 4,191,348 to Holwerda; U.S. Pat. No. 4,254,821 to Matsuda et al.; U.S. Pat. No. 4,573,802 to Kerrigan et al.; U.S. Pat. No. 4,826,107 to Thornton-Trump; U.S. Pat. No. 5,096,145 to Phillips et al.; U.S. Pat. No. 5,244,168 to Williams; and U.S. Pat. No. 5,845,848 to Amako et al., and of which are incorporated herein by reference.
Most of the glycol that is sprayed onto the wings falls off of the plane and flows into a drainage system which removes the de-icing fluid. An aircraft is typically sprayed with gallons of dilute and heated de-icing fluid that is used only one time.
Another drawback of certain prior art deicing fluids is the high chemical and biological oxygen demand that make them environmentally unfavorable. The glycols are exemplary of deicing fluids that particularly suffer from this type of environmental drawback, and most municipalities govern the amount of glycol-tainted water that can be released to local water treatment facilities.
It would be desirable to provide a recovery system that can collect and recycle both the water from glycol-containing water as well as the glycols from de-icing fluid sprayed onto an airplane so that both the water and the fluid can be reused.
Recycling the de-icing fluid would decrease the cost of spraying the aircraft by providing a recyclable product that may be used for a variety of alternative uses. Recycling the water from de-icing operations would also reduce overall costs by eliminating the cost to municipalities and the airports which must control the release of glycol-tainted water, as well as providing a beneficial use of the water at the airport location, saving the cost of using fresh water or water from the associated water authority. Another benefit of recycling the water recovered from RDAF is that the recovered water will not contain undesirable materials typically found in a municipal water supply (such as minerals, etc.).
Most attempts to adapt MVR for use in recycling glycol from de-icing operations have been less than completely successful as many such operations release treated water into the local sewer system or transport the treated water off-site.
Some prior art systems may use reverse osmosis in order to pre-concentrate the dilute glycol de-icing fluid prior to use of MVR.
Most other systems do not provide a resultant glycol concentrate at higher concentrations which may require further concentration of the fluid or, if the more dilute concentrate is shipped, will require greater shipping volume.
It would also be desirable to have such recycling occur in a continuous processing (or continuous batch processing) and to be able to produce two recycled products in the same operation at an airport site, without the environmental risk of releasing glycol-containing water to the local water shed or water treatment facility.
It is also desirable to be able to produce a glycol concentrate that can be efficiently shipped for reformulation into a variety of recycled products for other industrial uses.